Pluro-metallic rod



Sept. 3, 1935.' R. T.- HUMMEL 2,013,411

Sept. 3, 1935. T, HUMMEL 2,013,411

PLURo-METALLIC ROD Filed June 4,- 1932y 2 Sheets-Sheet 2 NFly- Z INVENTOR P05557 7.' HUMMEL A'ITORN Patented Sept. 3, 1935 stares si.. fi s amaai @ATENE @FFME PLURO-ll/LETALLIC ROD of Pennsylvania Application .lune 4, 1932, Serial No. 615,323

Claims.

This invention relates to an electrical conducting body comprising a plurality of joined unlike metals and to a process for producing the same.

In its more specific aspect the invention is directed to an anode adapted to be employed in an electron discharge device, and especially an X-ray tube, and to the process for producing an anode of this character having high electrical thermal conductivity characteristics, with the anode comprising a body7 portion having a target iirmly embedded therein, with the inter-- faces at the planes of Contact of said. target and said body lproper being a firm, tenacious, mechanical union and said body proper being free from blow holes and pipes.

Although my invention may nd application in Y fields other than the X-ray iield I shall describe the application of my invention in the X-ray ield for the sake of brevity and conciseness and so that the advantages of my invention may be clearly apparent to those skilled in the art.

X-ray tubes in general comprise an enclosing envelope containing a plurality of oppositely disposed electrodes therein. One of the electrodes, commonly termed the cathode, is ordinarily in the form of a lamentary body adapted to be heated to thermionic temperatures by means of an external source of electrical supply, as forV example, a secondary winding of a low voltage transformer. The other electrode of said tube, commonly termed the anode, generally comprises a solid body of copper or similar high heat and electrical conducting material, having a target, such as tungsten or the like, embedded in the face thereof opposite said cathode.

In order that X-rays of the desired wave length or frequency, or what is termed hardness, may be produced, there is applied between the incandescent cathode and the cold anode a voltage of stuilcient magnitude to cause the electrons to migrate with suicient velocity from the cathode to the anode. These electrons strike the target to produce X-rays. The hardness of the X-rays so produced depends upon the voltage applied between these electrodes. In the commercial operation of tubes of this character the voltage applied between the electrode terminals may be above 20,000 volts, and sometimesas high as 500,000 volts. l

It is Well known that when electrons ema hating from the cathode are directed to and strike the target to cause X-ray emanations therefrom, the target becomes heated. When the heat so developed in the target, due to the (Cl. Z50-35) electron bombardment thereof, is not readily dissipated in some manner the target will become overheated and ultimately fused and/or pitted, which effect is obviously undesirable.

These particular phenomena have heretofore 5 been appreciated by those in the art, as evidcnced by the anode constructions heretofore proposed for the purposes of attempting to provide an anode containing a target and which has high electrical and heat conductivity charac- 10 teristics. Prior to my invention a number of processes have been proposed for producing a unitary structure comprising a refractory metal embedded in a comparatively high thermal and electrical conductivity metal, such as copper or the like.

One of the methods heretofore proposed for this purpose contemplated uniting a low melting point metal of high electrical and heat conductivity characteristics, such as copper, to a relatively high melting point, high resistance metal, such as tungsten. The specic method suggested for uniting these two metals so as to obtain a juncture of good thermal conductivity and iirm mechanical characteristics between the low 5 melting point metal and the high melting point metal involved the following steps:

A refractory metal, as for instance tungsten, in the form of a button is placed in a suitable crucible and surrounded with a comparatively o large mass of copper metal, which is to become the body proper of the anode structure to be produced. This Crucible containing the refractory metal and the copper metal is placed in a reducing furnace containing an atmosphere of hydrogen gas therein. In the presence of this hydrogen, reducing, ambient the temperature of this Crucible, together with its constituents, is elevated so that it is higher than that necessary to fusethe copper so that the copper ows over the tungsten, and in such a fluid condition that it may wet the same. Thereafter the resultant mass is allowed to cool and the bly-metallic structure is extracted from the Crucible.

It has been found that the bi--metallic structure produced in this manner exhibits at least one desirable property, namely, that of a strong mechanical union at the joint. Although exhibiting this desirable property this bi-mei-,allic structure is not suitable for all purposes, and

especially for X-ray anode purposes, because of the internal physical characteristics of the copper body.

Upon shearing the copper of said bi-metallic slug either lengthwise or cross wise it is generally I found that its internal structure has a relatively large number of small voids, sometimes simulating a honeycomb, and commonly termed blow holes, and/or one or more large cavities, commonly referred to as piping. i

One other method heretofore proposed for the same general purpose contemplates the substitution of the hydrogen reducing ambient with an ordinary atmospheric ambient. Bi-metallic elements comprising a refractory metal, as for example tungsten, having its bott-om and sides coated with a relatively low melting point metal, asfor example copper, produced according to this method, have not been satisfactory for X-ray anode purposes, although the copper of said structure is a homogeneous mass, substantially free from blow holes and piping.

Although the employment of the latter method overcomes the disadvantages inherent in the method utilizing the hydrogen ambient so as to eliminate the voids or cavities, it is found that the resulting product lacks the advantages of firm mechanical union at ther juncture of the tungsten and the copper, which is provided by employing the method using the hydrogen ambient.

It is apparent that in an oxidizing medium, such as an atmospheric ambient, the tungsten will become coated with an external thin lm or skin of oxide, which prevents a complete wetting of said tungsten at the surfaces of contact between said tungsten and said copper.

. This is my explanation of the lack of a firm, tenacious mechanical union between said tungsten and said copper. The oxide lm also acts as a heat and electrical insulator to prevent the heat and electrical energy from being very quickly conducted between the tungsten and the copperVthe latter of which hasgood heat capacity and electrical conductivity characteristics.

vI n order that these disadvantages as well as others may be effectually obviated, I have devel-V oped the following invention.:

` In its briefest aspect the invention is directed to the provision of a new type of pluro-metallic structureand especially a structure of this character particularly adapted to be employed as an Xeray anode. 4This novel structure is preparedVY by my novel method which includes coating a refractory metal, such as tungsten, with a layer of a high conductivity metal, such as copper, in a reducing atmosphere, as for example hydrogen. The. bi-metvallic slug thus prepared is united by suitableV pressure means to a relatively large mass l of a high conductivity metal.

One object of my invention is to provide Va novel pluro-metallic structure free from a substantial quantity of voidsand including a refractory metal and a high conductivity metal.

Another object of my invention is to provide a novel X-ray anodestructure.

A further object of my invention is to provide a novel method for providing a pluro-metallic structure.

A still further object of my invention is to provide a novel method for providing an X-ray anode.

`Other objectsvand advantages of my invention will become readily apparentfrom the following description taken in conjunction with the appended drawings. Figure, 1, represents a. verticalgcross section, with a portion thereof in elevation, of a fragment of a pluro-metallic structure and especially anX- ray anode embodying my invention.

Figure Zfrepresents an illustration of the particular association of parts that is utilized in carrying out my invention and serves to illustrate one of the steps of my process.

Figure 3 represents a later stage in the process of carrying out my invention.

Figure 4 illustrates the means employed to formr the slug.

Figure 5 represents a slug utilized'in forming a pluro-metallic structure.

Figure 6 is a modification of Figure l.

Figure 7 is a modification of Figure 2.

Although my invention is broadly directed to 'oi-metallic structures and to the process of producing the same, for the sake of simplicityA of description and ease of understanding, and bev cause it embodies X-ray anodes and is especially applicable thereto, I will describe my invention as applied to an X-ray anode and to the processI of producing the same. Y

According to my invention I take a rare refractory metal i, suchv as tungsten or the 'like,`

cal or other treatment in order that they may be substantially freed from any oxide or other coating, which might prevent the coppe-r from forming a tenacious bond thereat. Thereafter in order that I may obtain this firm, tenacious bond betweeny the tungsten and the metal, copper, Y

which is to be united therewith and so that the juncture between the adjacent faces of the tungsten and copper may be of high heat and thermal Aconductivity characteristics, the tungsten button is coated with a layer of molten copper in an atmosphere of hydrogen.

One means suitable for carrying'out this step, and employed herein so that a clear understanding of my invention may be ascertained, corn-V prises a furnace iii having gas tight walls and composed of any suitable refractory heat insulating material. Resting on a plurality of spaced supports on the base of said furnace is a crucible il, composed of graphite or the like. The interior diameter of this crucible i I is slightly greater, and preferably about three quarters of an inch greater than the diameter of the button, which in this case happens` to be of a circular peripheral configuration. v

Snugly fitting along the sides vof this crucible and having its lower surface located on the upper surface of the base of this crucible, is a removable plate i2 composed of the same material as the crucible per se. Embedded in this plate i2, diametrically opposed and spaced from the center thereof, a distance approximately one-half that of the diameter of the button l, are a plurality of relatively thin bent wires i3, preferably of the same composition as said button.

Said button l is placed in the crucible' with the face to b e exposed adjacent the upper surface of the plate i2, and is preferably so positioned that its center is in approximate contiguity with the center ofthe plate i2. The bent tungsten wires i3 extend toward each other and lap on to the upper face of said buttonri to hold said button in position during the performance .of the one step of my invention.

Afterthe button is placed within the crucible an appropriate Vquantity of 'commercially pure copper fragments, and preferably a quantity whose volume is relatively great, and about ten times as greatas the volume of the tungsten button, is placed upon said button and in said crucible.

' Prior to the heating of said metals and at this stage hydrogen gas is continually admitted into said closed chamber through a conduit lli and allowed to egress therefrom through a conduit l5. Heat is now applied to said chamber by any appropriate means, as for example any suitable resistance element or other means (not shown). The heating operation is maintained and hydrogen is allowed to pass through the furnace by Virtue of the conduit ii and the outlet i so that the copper fragments in the Crucible may be heated to a temperature suiciently high to cause the copper to become suciently molten to ilow over the exposed surfacel of said button and Wet said surfaces.

Instead of placing fragments of solid copper in the crucible together with thel tungsten button, I may, in the presence of hydrogen, first heat the button l to a temperature above the melting point of copper and about li50 C. When this temperature is attained suiiicient molten copper in the presence of hydrogen is added directly to te Crucible.` This temperature may be maintained fora short period of time and the heating is removed and the hydrogen is turned oil at lf3.

The crucible together with its contents is allowed to cool to room temperature. The entire contents of the Crucible including the removable graphite plate E2 may then be extracted therefrom en masse. The graphite plate i2 may be detached from the metallic structure by serving the tungsten wires at the point of juncture of said plate and said button leaving a slug 5 composed of a tungsten button I having its bottom and side Walls coated with a layer 2 of copper metal, with the volume of said copper metal being relatively great and about ten times as great as the Volume of said tungsten button. The juncture of said tungsten button and said copper metal of this slug is mechanically strong and has high thermal and electrical conductivity characteristics.

When copper is applied to said button in this manner there generally appear small pipes or blow holes extending in the direction of the depth of the copper and generally considerably abo-ve the surface skin of the copper, in contact with the tungsten button. These blow holes or pipes are ordinarily apparent to the eye and in order that the slug 5 may be prepared for the next step the slug is machined down to eliminate most, and generally all, or" the pipes or blow holes.

Instead of detaching the copper coated button i from the plate ifi prior to machining, the button l may be machined while attached to said plate and thereafter the plate may be removed therefrom.

The next step of the process may involve the preparation of the body proper of the anode, bearing the reference character 3. This body proper 3 may be composed of commercially pure d'eoxidized copper, which is free from blow holes or pipes` This copper rod 3 is generally prepared by casting deoxidized copper in the air and allowing it to cool. The copper rod 3 is of appropriate length depending upon the length of the anode desired and generally has a length which is more than about twice, and generally about eight times the depth of the copper coating 2 in which the button i is embedded. The diameter of this rod 3 may be about three eighths of an inch greater than the corresponding dimension of the slug 5 in order that the slug may be iirmly united with the copper body 3 in a manner hereinafter more fully described.

After the copper rod 3 is cast, one end thereof is machined out so as to provide a recess with the depth and diameter of said recess being equal to the corresponding dimensions of the slug 5. The slug 5 containing the tungsten target or button is in the following manner rmly united with said copper body S and firmly locked therewith to provide a substantially unitary structure. For this purpose I may employ any suitable pressure means, as for example a hydraulic press (not shown), embodying a platen 2i! and a force 2i located thereabove. Between said platen and force is located a cylindrical steel die 6 whose internal dimension is approximately equal to the corresponding external dimension of the copper rod 3. The length of this die may be equal to the sum oi the length of the copper rod 3 and the depth of an annular plate 22.

In carrying out my invention the copper rod S is inserted into the opening of the die S with the recessed end of said rod being uppermost and extending towards the force 2i.

Into the recess in the upper part or" the rod 3 is inserted the slug 5 containing the tungsten button, which slufr rits snugly in said recess. Thereafter the annular ring 22, whose thickness is about three sixteenths of an inch and equal to the corresponding dimension of the cylindrical portion surrounding the recess in the rod 3, is placed in the die and rests upon the tube of the rod 3.

A plunger 23, whose external diameter is equal to the corresponding internal dimension of the annular ring 22 and whose length is substantially greater and about 3 or l times as great as the depth of the annular ring 22, is inserted into the opening of said ring and rests upon the upper face of said slug. Thereafter the force 2| is moved downwardly and upon the plunger 23 with a sucient force to cause the copper 2 of the slug 5 to belly outwardly and attain a substantial barrel shape, and further to cause the metal in the annular portion 4 to flow around and upwardly along the plunger 23, as shown in Figure 3. A force of about sixty tons is applied to said slug 5 whereby to cause this action to take place. Thereafter the plunger 23 and the annular ring 22 are removed and the rod, as illustrated in Figure 1, is also removed from the die. The last operation is essentially a machining operation in order to remove the extraneous annular portion of copper formed when this metal flowed around the plunger 23.

The anode so prepared comprises a body 3 of copper having a barrelled recess in which is interlocked a barrel shaped slug 5, composed of copper, with the slug 5 having firmly and tenaciously united thereto a tungsten target I. The union between the rod 3 and the slug 5 is such that the slug 5 may not be readily removed from the rod 3 and the interfaces of said rod and slug are in close contiguity.

A modication of the preferred form of my invention heretofore described is illustrated in Figures 6 and 7. Figure 7 shows a slug consisting of a target 3B of tungsten embedded in a body of copper 3l. The body of copper has a dovetailed portion 32 adapted to be inserted in the recess of the cylindrical body portion, as shown. This slug may be prepared in a hydrogen furnace by following the method hereinbefore outlined to obtain a tenacious and rm mechanical union between the copper and tungsten. Thereafter pressure. is applied to the copper body and slug whereby the copper in the slug and that in the body proper is caused to flow to provide a dovetailed interlocking structure as shown in Figure 6.

The invention is not to be limited to the exact details as described, but only by the prior art.

What is claimed is:

l. The method of preparing an X-ray anode comprising placing in a cylindrical recess of a copper body another copper body of cylindrical contour to which is tenaciously united a refractory metallic body and applying pressure to said bodies to cause the coniiguration of said recess and said second mentioned copper body to change from that of a cylinder to that of a barrel with bulging sides for interlocking said second mentioned body to said iirst mentioned body.

2. The method of preparing an X-ray anode comprising forming a slug by coating a tungsten body with a copper body in a hydrogen atmosphere, machining said slug, placingl said slug in a recess of a copper body whose volume is large as compared to that of said slug and applying pressure to said slug to cause the configuration of said slug and recess to simulate a barrel having bulging sides for interlocking said slug to said body.

3. A pluro-metallic structure comprising a body of metal of high electrical and thermalv blow holes, said body of metalY having a recess at one end thereof, the cross vsectional areas of said recess taken on planes at right angles to the longitudinal axis of said body along 'a major continuous portion of said recess intermediate its ends being substantially greater than the cross sectional area of said-recess at the outer ends thereof, and another metallic body of high thermal and electrical conductivity'characteristics in said recess, said other metallic body having a configuration substantially complementary to that of said recess and'having a refractory metallic body tenaciously united therewith. Y Y

5, An X-ray anode comprising a body of copper substantially free from pipes and blow holes, said body of copper having a recess at one end thereof, said recessv having a conguration simulating a barrel with bulging sides, andrancther copper body in said recess, said other metallic body having a conguration substantially oomplementary to that of said recess and having a tungsten body tenaciously united therewith.

ROBERT T. .HUMMEL 

